I have never thought to score games out of 10. So none. I don't think any game is perfect or can't be improved on, anything I could say that is 10 out of 10 would be a blatant lie.
No game is 10/10.
You could just redefine 10/10 to be "as good as a games get" or possibly, "a paragon for what games like this should be." or something like that.
No reason it has to mean perfect.
A 10/10 could mean that it is better than 90% of all commercially released games.
It could mean that it ranks in the top 10% of video games you played.
It could mean a thousand different things.